The field of the invention relates generally to rotors of turbines in a gas turbine engine and, more particularly, to methods and apparatus for retaining a damper in turbine ceramic matrix composite (CMC) blades.
At least some known aircraft are driven by two or more gas turbine engines that include turbine sections that include a plurality of blades, sometimes referred to as “buckets”, mounted to the periphery of a rotor wheel or disk in an angularly spaced relationship to each other. The turbine blades of typically plural rotor disk stages project into an axially flowing hot gas stream to convert the kinetic energy of this working fluid to rotational mechanical energy. To accommodate material growth and shrinkage due to variations in temperature and centrifugal forces, the blades are typically provided with roots having a “fir tree” configuration, which are captured in dovetail slots in the rotor disk periphery. Typically, turbine blades include a platform to which the root, or dovetail is coupled. Also, typically, turbine blades include an airfoil coupled to the platform.
During engine operation, vibrations are induced in the turbine blades, including side-to-side, i.e., circumferential movement of the turbine blade platforms that increase excitation stresses induced in the turbine blade shanks. If left unchecked, these vibrations can result in premature fatigue failures in the blades.
To dissipate the energy of these vibrations, and hence lower vibrational amplitude and associated stresses, it is common practice to dispose dampers between the blades and the disk or between adjacent blades in positions to act against surfaces of tangentially projecting blade platforms. When the turbine disk rotates, the dampers are pressed against the platform surfaces by centrifugal forces. As the blades vibrate, the damper and platform surfaces slide against each other to produce frictional forces effective in substantially absorbing and thus dissipating much of the vibrational energy.
Also, in at least some aircraft gas turbine engines, the blades are formed from a ceramic matrix composite (CMC), such as silicon carbide (SiC). Such CMC materials may operate with a higher temperature working fluid, thereby facilitating a greater rate of energy conversion than similarly-sized high-temperature metal alloy blades. Therefore, blades formed from CMCs are substituted for high-temperature metal alloy blades because of the CMC blades' increased operating temperatures. However, such CMC blades have a lower ductility and strain tolerance than the high-temperature metal alloy blades they replace and known damper apparatus may not be suitable for damping the vibrations induced within the CMC blades.